1. Technical Field
The present invention relates to an interrupt control circuit, a circuit board, an electro-optic device, and an electronic apparatus.
2. Related Art
There is disclosed an example of an interrupt control circuit for performing interrupt control to a central processing unit (CPU) in, for example, Illustrated Introduction to Z80 Microcomputer Application System for Hardware, Second Edition, pp. 186. This interrupt control circuit is composed of an OR circuit for outputting an interrupt signal, which is a logical OR signal of a plurality of interrupt cause signals input from the outside, to the CPU, and an interrupt vector generating circuit for outputting, to the CPU, an interrupt vector signal corresponding to the interrupt cause signal. For example, in the case in which the CPU is provided to a personal computer; the interrupt cause signals are output from a mouse, a keyboard, and so on. It should be noted that the interrupt vector signal denotes a signal indicating an address on the memory where an interrupt processing program to be executed by the CPU correspondingly to the interrupt cause signal is stored.
When at least one of the plurality of interrupt cause signals are controlled to be in a high level, the OR circuit outputs the interrupt signal of a high level to the CPU. An interrupt vector generating circuit outputs the interrupt vector signal corresponding to the interrupt cause signal controlled to be in a high level to the CPU. Here, when two or more of the interrupt cause signals are controlled to be in a high level, the interrupt vector generating circuit outputs, to the CPU, the interrupt vector signal corresponding to the interrupt cause signal with a higher priority along an order of priority determined previously. When the interrupt signal of a high level is input in the CPU, in other words, the CPU recognizes occurrence of the interrupt request, the CPU executes the interrupt processing program stored in the address on the memory indicated by the interrupt vector signal, thus performing the interrupt processing.
The interrupt control circuit and the CPU are synchronous circuits operating with a common clock signal, in which the interrupt control circuit outputs the interrupt signal in sync with the clock signal, and the CPU monitors the state of the interrupt signal input from the interrupt control circuit with a predetermined timing specified with the clock signal, and performs the interrupt processing if the CPU recognizes the state of the interrupt signal as a high level with that timing.
As described above, in the case with the synchronous circuit in the related art, since the monitoring process of the interrupt signal is required, the power consumption of the CPU increases, and further, since all of the operation timings are specified with the clock signal, the operation speed is low. On the other hand, in recent years, an asynchronous circuit without requiring a common clock signal draws attention as a measure for realizing a high speed and low power consumption electronic circuit. However, as described above, since the interrupt control circuit in the related art requires the clock signal common to the CPU, it is difficult to perform the interrupt control to an asynchronous type of CPU. Therefore, the asynchronous CPU can hardly be used, thus it is difficult to realize a high speed and low power consumption interrupt control circuit.